Good news, I just had the EGR replaced and it the idle is finally normal! I put about 20 miles on it in stop and go traffic and a few WOT runs. I will be putting on more miles tomorrow and keep my fingers crossed that it will remain smooth. The car seems like it is much smoother during acceleration and idles at about 500-550 RPM's. This still seems a little low to me, does anyone know the normal idle RPM's are for our cars?

Thats great news, how much did it cost?
I'm going to look into it as well

The EGR was $120 and Labor was $120 total $240.00

As Rodney mentioned it can be done if you have the tools and basic knowledge but in my case it was such a PITA to get to I just took it to a local guy and had him do it.

That's a good price.
I've been getting prices around $250 just for the part.

Try this:
http://www.partstrain.com/ShopByDepartment/EGR_Valve/MERCEDES_BENZ/CLK500

http://www.thepartsbin.com/guides/me...egr_valve.html

Thx, I'll order one ASAP and let everyone now the result.

Good news, I put a few hundred miles on the new EGR and the idle is still smooth, and it seems to be more responsive at various RPM's. The idle still seems low at 500 RPM's and at times will randomly raise to about 600 RPM's with a healthy deep idle sound. I am wondering if this has to do with a MAF going bad as Rodney suggested.

That's awesome!
you mentioned your idle seems low. Mine is right in that range too, it has been since I got the car, I always thought that was normal.

My 5.5 idles right at 500rpm. I'd actually like it to bump up to 600 because it "lumbers" a bit and I feel it, even with new motor mounts. But it's a big V8, so I expect to feel it working.

Okay guys now whats the freakn name for the part in german language?

Need to TLC my baby, too ! ;-)

I just finished changing the EGR. I will report back with the result.

ok so changing the EGR finally fixed my problem!!!
the car runs way smother now and like D-MAN said its definitely more responsive.
hopefully this will e the end of the rough idle from now on.

Did you guys also change the tube/pipe (whatever you want to call it) when replacing the EGR, my indy said it was necessary and quoted me $160 for EGR, $100 for the tube and 2 hours of labor.

Sorry I have been off the grid for a while, I did not end up changing the tube. My guy said it was a lot of work to get the EGR off without damaging the tube but he was able to do it.

Hey JP how is the car running?

Hey D-MAN I've been off the grid for a while too, just getting ready to pull the car out of winter storage. hopefully the rough idle won't come back.

well it looks like all the work I have done last year was for nothing.
the rough idle is back with the hesitation on acceleration and the knocking is worse than ever.

not sure what I'm going to do with this car now.

So the EGR didn't fix it?

I'm having the same issue. New plugs / wires woke it up but didn't fix the idle. Cleaned the MAF, no dice. Air filters are new. I thought the EGR was closed at idle so it wouldn't be an issue. How did the part look when you pulled it out?

i also have a misfire feeling to idle. Changed plugs, wires, and cleaning maf this week. praying that helps.

Best gas to use in clk550 would v power shell gas be worthy

Found this thread and was wondering if anyone had any luck figured out there problem and what was the fix?

Had this issue with my 550. I had an extended warranty so I took it to the dealer. They found both engine mounts to be leaking as well as a broken transmission mount. I was also getting a code for retarded cam timing on one cylinder bank which was one of the magnetic sensors, a common problem. The "rough idle" was gone after these repairs, apparently the engine was just a little too free to hop around!

I had a very slight vibration at idle with no real noticable hesitation under acceleration. When my car was in getting an ATF flush the dealer also pulled the codes. They noted a misfire on cylinder 3. I had already (prior to this visit) changed all the plugs as the car was on 100k. So I changed the coilpack and spark plug cables on cylinder 3 and it was super smooth after that.

I had a very similar sounding issue on my 280. Turned out to be the coil on cylinder 1. So get those and the plugs checked.